1. Field of the Invention
The present invention relates generally to a control device for an internal combustion engine. Specifically, the present invention relates to a control device for controlling intake and exhaust valves of an internal combustion engine.
2. Description of the Related Art
The present disclosure relates to improvements in a device for controlling opening and closing of intake and exhaust valves of an internal combustion engine as set forth in co-pending related U.S. patent applications Ser. Nos. 08/077,509, 08/077,510 now U.S. Pat. No. 5,365,896, and 08/008,801, now U.S. Pat. No. 5,333,579 filed by the present applicant.
For explaining the task of the present invention, one type of conventional device for controlling intake and exhaust valves of an engine will be described hereinbelow with reference to FIGS. 8 and 9.
Japanese Utility Model 57-198306 discloses a cam 2 which is rotatably disposed about a cam shaft 1. The cam 2 functions to open an intake valve 16 against a biasing force of a valve spring 17 (FIG. 8) with the aid of a rocker arm 15. As may be seen in FIG. 9, the cam 2 is positioned axially along the cam shaft 1 between a cam shaft receiving bracket 3 and a flange member 5 which is secured to the cam shaft 1 by means of a key 4.
The cam 2 has at one end thereof a flange portion 7 which is formed with a generally U-shaped recess 6. The above-mentioned flange member 5 is also formed with a generally U-shaped recess 8.
Between the flange member 5 and the flange portion 7, there is disposed an annular member 9. The annular member 9 has disposed at diametrically opposed portions thereof pins 10 and 11 which slidably engage the U-shaped recesses 6 and 8. The annular member 9 has a cylindrical outer surface rotatably supported by a control ring 12. As is seen from FIG. 8, the control ring 12 has, at an outer peripheral portion thereof, a projection 12a which is rotatably held in a supporting bore 13 formed in a cylinder head. The control ring 12 has, at a portion diametrically opposed to the projection 12a, an arcuate toothed portion 12b which engages a toothed ring 14a provided around a rocker shaft 14.
The control ring 12 is urged to pivot back and forth in the supporting bore 13 by a drive mechanism (not shown) via the toothed ring 14a and the toothed portion 12b. As seen in FIG. 9, an inner annular surface 9a of the annular member 9 faces an outer annular surface 5a of the flange member 5 with a space 18 defined therearound for allowing eccentric movement of the annular member 9 relative to the camshaft 1.
For example, during low speed shifting of the engine, a fluid pressure actuator (not shown) the driving mechanism (not shown) is active to move the rocker shaft 14 in a first direction thus the toothed portion 14a of the rocker shaft is moved such that the control ring is pivoted at the projection 12a thereof causing the annular member to be moved eccentrically to the axis `C` of the camshaft. Similarly, during high speed shifting of the engine the fluid pressure actuator (not shown) urges the rocker shaft 14 in the opposite direction so as to move the annular member 9 via the control ring 12 in the opposite direction so as to be disposed eccentric to the axis C, angularly displaced therefrom in the opposite direction from the eccentric displacement effected during downshifting.
That is, when the center `C` of the annular member 9 assumes the position as shown in FIG. 8, the cam shaft 1 and the annular member 9 are coaxially aligned. Thus, under this condition, the annular member 9 rotates synchronously with the cam shaft 1 due to engagement between the pin 11 and the U-shaped recess 8, and the cam 2 rotates synchronously with the cam shaft 1 due to engagement between the pin 10 and the U-shaped recess 6.
When in response to engine operation, the rocker shaft 14 supporting the rocker arm 15 is rotated by the drive mechanism (not shown), the control ring 12 is pivoted in a given direction using the projection 12a as a fulcrum. With this, the center `C` of the annular member 9 becomes eccentric to the cam shaft 1. Accordingly, the pins 10 and 11 are slid in and along the respective U-shaped recesses 6 and 8, and the flange member 5 and the flange portion 7 are pivoted around the cam shaft 1. Thus, each time the cam shaft 1 makes one turn, the rotation phase of the annular member 9 relative the cam shaft 1 is changed and, at the same time, the rotational phase of the cam 2 relative the annular member 9 is also changed. Accordingly, the cam 2 rotates relative to the cam shaft 1 with a phase difference determined according to the eccentric displacement of the annular member 9 relative to the cam shaft 1. Thus, the valve timing can be varied in accordance with the phase difference of the cam 2.
According to this, at low speed ranges, the valve opening timing of the intake valve is slowed while the valve closing timing is advanced such that an interval during which opening of the intake valve overlaps opening of an exhaust valve becomes short for promoting combustion and low speed torque. On the other hand, at high speed ranges, the eccentric movement of the annular member 9 controls the valve timing such that an opening timing of the intake valve is advanced and a closing timing thereof is slowed and a time at which the opening of the intake and exhaust valves overlap becomes long, for obtaining high power output.
According to this, when the annular member 9 is moved eccentrically to the cam shaft 1 a width L1 of the space between the outer annular surface 5a of the flange portion 5 and the inner annular surface 9a of the annular member 9 becomes small at one side of the flange member 5 and a degree of eccentric movement of the annular member becomes limited according to a thickness of the flange member. Thus a large degree of eccentric displacement of the annular member is not possible according to the conventional structure.
Accordingly a large rotational phase difference between the annular member 9 and the cam shaft 1 is not possible and thus large variation in angular velocity may not be imparted to the cam 2 and a range of valve timing control is limited to a substantially small range. This problem may be alleviated by by reducing a circumference of an outer annular surface 5a of the flange portion 5 or alternatively by enlarging and inner annular surface 9a of the annular member 9, for example.
Thus it has been required to provided a control arrangement for moving an automotive cam 2 relative a cam shaft 1 thereof which allows substantially large variation of rotational phase of the cam 2 relative the cam shaft 1.
Also, according to the above arrangement, since movement off the annular member 9 controls the rotational phase of a single cam 2, in high performance engines, for example, where a large number of valves are present, such as engines which may have a pair of intake valves and a pair of exhaust valves for every cylinder, providing such a control arrangement as described above requires a substantially large space and large number of parts, and of course, larger costs.